Field of the Invention
The present invention relates to the field of the control of gear shifts in a gearbox.
More specifically, it relates to a method of and device for synchronizing the speed common to two concentric primary shafts of a hybrid transmission cumulatively receiving the torque from a combustion engine and the torque from an electric machine in a hybrid mode of operation in which these two shafts are rotationally connected by a first coupling means, with the speed of a secondary transmission shaft bearing at least one idler pinion. The synchronization proposed allows one of these pinions to be coupled to its shaft by closing a second coupling means that does not have mechanical synchronizing members.
This invention applies non-limitingly to a hybrid transmission for a motor vehicle provided with a combustion engine and with an electric drive machine, comprising two concentric primary shafts each bearing at least one gear transmitting to a secondary shaft connected to the wheels of the vehicle and a first means of coupling between two primary shafts that can occupy three positions, in which positions: the combustion engine is uncoupled from the drivetrain connecting the electric machine to the wheels, it drives the wheels with or without top-up from the electric machine, or it is coupled to the electric machine so that their torques can be combined.
Description of the Related Art
FIG. 1 describes a non-limiting example of a hybrid transmission using this design principle. This transmission, illustrated in publication WO2012/131259, comprises a solid primary shaft 1 connected directly by a filtration system (damping hub, damper, double fly wheel or the like) 2, to the inertia flywheel 3 of a combustion engine (not depicted). The solid shaft 1 bears an idler pinion 4 that may be connected therewith by a first coupling system 5 (dog clutch, synchromesh, or other type of progressive or non-progressive coupling). A hollow primary shaft 6 is connected to the rotor of an electric machine 7. The hollow shaft 6 bears two fixed pinions 8, 9. It may be connected to the solid primary shaft 1 by means of the first coupling system 5. A secondary shaft 10 bears two idler pinions 11 and 12. The idler pinions 11, 12 may be connected to the primary shaft by way of a second coupling system 13 (dog clutch, synchromesh or other type of progressive or non-progressive coupling). The secondary shaft 10 also bears a fixed pinion 14 and a pinion 15 transmitting to a differential 16 connected to the wheels of the vehicle.
As indicated earlier on, the first coupling means 5 can occupy at least three positions in which:                the combustion engine is uncoupled from the drivetrain connecting the electric machine 7 to the wheels (sliding gear in the middle as in FIGS. 1, 2 and 3),        the combustion engine drives the wheels with or without top-up from the electric machine (sliding gear to the left), and        the combustion engine and the electric machine 7 are coupled in such a way that their respective torques are combined and sent to and the wheels (sliding gear to the right).        
In hybrid mode (cf. FIGS. 2 and 3), the electric machine drives the hollow primary shaft 6 whereas the solid shaft receives the torque from the combustion engine. The gearbox has two hybrid gear ratios referred to as “town” and “highway”, in which the torque is transmitted to the secondary shaft 10 via the fixed pinions 8 or 9 or no 7. To shift from one of these two ratios to the other, the box has the second coupling system 13. In the absence of synchronizing rings, a system that uses a dog clutch to couple the sliding gear with the pinions requires precise control of the primary speed by the electric machine and/or the combustion engine in order to avoid jerks in the flow of torque.
Publication FR 2 933 247 discloses a method for coupling a shaft of an electric machine with a wheel shaft for an electric or hybrid vehicle. The method described involves the following steps:                the electric machine is fed a speed setpoint corresponding to the speed of the wheel shaft, disregarding the stepdown ratio between the shaft of the electric machine and the wheel shaft,        when the speed of the shaft of the electric machine reaches a calibratable threshold, a zero torque is applied to it and a mechanical synchronizing device is actuated so as to equalize the speed of the shaft of the electric machine with the speed of the shaft connected to the wheels, and        as soon as the speed of the shaft of the electric machine is equal to the speed of the shaft connected to the wheels (disregarding the stepdown ratio), dog-clutch engagement is performed.        
With this method, the electric machine is made to operate first of all in order to reach a speed close, but not exactly equal, to that of the shaft connected to the wheels; a synchronizing device then completes the equalizing of the speeds between the two shafts, and then the speed ratio is finally engaged by dog-clutch engagement.
It has already been proposed for the idler pinions on a shaft of a gearbox without a mechanical synchronizing member to be synchronized by simply modulating the torque transmitted to these pinions so as to equalize their speed with the shaft prior to mechanical coupling.
However, in the case of a hybrid vehicle gearbox with concentric primary shafts driven by two power sources which are distinct, but connected to one another by a coupling means, the inertia caused by the machine during certain phases of the gear shift in hybrid mode, includes the combustion engine. The inertia to be overcome by the electric machine is then temporarily multiplied by a factor of ten, leading to torque saturations for this machine.